Yup, dished pistons with a 1.5 head don't yield too high a compression ratio...about 8.8:1. Even with flat-tops you're under 11:1!
No problem with pump gas, and the chamber/piston design is pretty efficient as far as 'squish' goes. Should be able to run 87 octane with that combo quite easily, as long as you don't add too much total ignition timing. I'd deburr the chamber edges to be safe.
I ran 89 octane with a stock hydraulic cam and 9.8:1 (flat-tops with milled 1.9
H head), and it was great. It would *barely* ping with 87 so I bumped it a few octane points. I'm referring to the same shortblock I loaned you for your *Labatt's blue* wagon Gary.
Bob